1. Functional Reactive
Programming
with
ReactiveCocoa
@EliSawic

2. About me
Eliasz Sawicki
Blog: www.eliaszsawicki.com
Twitter: @EliSawic
@EliSawic

3. Agenda
• What is functional reactive programming?
• Working with streams
• ReactiveCocoa - Thinking in signals
• Example
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4. Functional Reactive Programming
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5. Wikipedia
Functional reactive programming (FRP) is a programming
paradigm for reactive programming (asynchronous dataflow
programming) using the building blocks of functional
programming (e.g. map, reduce, filter).
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6. Reactive
Programming
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7. C = A + B
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8. C = A + B
A B C
1 2 3
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9. C = A + B
A B C
1 2 3
1 5 6
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10. Functional
Programming
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11. Blocks
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12. Functional
Reactive
Programming?
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13. Reactive
Programming?
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14. Imperative
vs
Declarative
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15. Imperative
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16. Imperative
let array = [0, 1, 2, 3, 4, 5]
var evenNumbers = [Int]()
for element in array {
if element % 2 == 0 {
evenNumbers.append(element)
}
}
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17. Declarative
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18. Declarative
let array = [0, 1, 2, 3, 4, 5]
let evenNumbers = array.filter { $0 % 2 == 0 }
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19. Working with streams
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20. Stream
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21. Manipulating streams
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22. Map
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23. Filter
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24. Aggregating
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25. Manipulating
multiple streams
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26. Combine latest
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27. Composable
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28. Composable
stream.filter {}
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29. Composable
stream.filter {}
.map {}
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30. Composable
stream.filter {}
.map {}
.reduce {}
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31. Composable
stream.filter {}
.map {}
.reduce {}
.map {}
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32. www.rxmarbles.com
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33. ReactiveSwift
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34. ReactiveCocoa
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35. Thinking in Signals
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36. What is a signal?
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37. This screen is a signal
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38. Represents events
over time
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39. Observing does not
trigger side effects
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40. No random access to
events
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41. Observe
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42. @EliSawic

43. If you don't listen, it's
gone
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44. What is event?
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45. Non-Terminating
• Next
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46. Terminating
• Completed
• Failed
• Interrupted (Reactive Cocoa)
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47. Location Service
protocol LocationServiceDelegate {
func locationService(locationService: LocationService, didUpdateLocation update: LocationUpdate)
}
class LocationService {
var delegate: LocationServiceDelegate?
private func onUpdate() {
let update = LocationUpdate()
delegate?.locationService(locationService: self, didUpdateLocation: update)
}
}
@EliSawic

48. Location Service
class LocationService {
private func onUpdate() {
let update = LocationUpdate()
NotificationCenter.default.post(name: "LocationUpdate", object: update)
}
}
@EliSawic

49. Location Service
class LocationService {
let locationUpdates: Signal<LocationUpdate, NoError>
private let locationUpdatesSink: Signal<LocationUpdate, NoError>.Observer
init() {
(locationUpdates, locationUpdatesSink) = Signal<LocationUpdate, NoError>.pipe()
}
private func onUpdate() {
let update = LocationUpdate()
locationUpdatesSink.send(value: update)
}
}
@EliSawic

50. Location Service
class LocationService {
let locationUpdates: Signal<LocationUpdate, NoError>
private let locationUpdatesSink: Signal<LocationUpdate, NoError>.Observer
init() {
(locationUpdates, locationUpdatesSink) = Signal<LocationUpdate, NoError>.pipe()
}
private func onUpdate() {
let update = LocationUpdate()
locationUpdatesSink.send(value: update)
}
}
@EliSawic

51. Location Service
class LocationService {
let locationUpdates: Signal<LocationUpdate, NoError>
private let locationUpdatesSink: Signal<LocationUpdate, NoError>.Observer
init() {
(locationUpdates, locationUpdatesSink) = Signal<LocationUpdate, NoError>.pipe()
}
private func onUpdate() {
let update = LocationUpdate()
locationUpdatesSink.send(value: update)
}
}
@EliSawic

52. Location Service
class LocationService {
let locationUpdates: Signal<LocationUpdate, NoError>
private let locationUpdatesSink: Signal<LocationUpdate, NoError>.Observer
init() {
(locationUpdates, locationUpdatesSink) = Signal<LocationUpdate, NoError>.pipe()
}
private func onUpdate() {
let update = LocationUpdate()
locationUpdatesSink.send(value: update)
}
}
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53. Observing
locationUpdates.observeValues { update in
// react to update
}
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54. Manipulating
let homeUpdates = locationUpdates.filter { update in
isHomeArea(update)
}
homeUpdates.observeValues { update in
presentAlert("Welcome home")
}
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55. Manipulating
let homeUpdates = locationUpdates.filter { update in
isHomeArea(update)
}
homeUpdates.observeValues { update in
presentAlert("Welcome home")
}
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56. Signal producer
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57. Represents a tasks
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58. Possible side effects
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59. Does not start it's
work if not asked
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60. HTTP request
func fetchUser() -> SignalProducer<User, FetchError> {
return SignalProducer { observer, _ in
// fetching user
let user = User()
observer.send(value: user)
observer.sendCompleted()
}
}
@EliSawic

61. HTTP request
func fetchUser() -> SignalProducer<User, FetchError> {
return SignalProducer { observer, _ in
// fetching user
let user = User()
observer.send(value: user)
observer.sendCompleted()
}
}
@EliSawic

62. HTTP request
func fetchUser() -> SignalProducer<User, FetchError> {
return SignalProducer { observer, _ in
// fetching user
let user = User()
observer.send(value: user)
observer.sendCompleted()
}
}
@EliSawic

63. HTTP request
func fetchUser() -> SignalProducer<User, FetchError> {
return SignalProducer { observer, _ in
// fetching user
let user = User()
observer.send(value: user)
observer.sendCompleted()
}
}
@EliSawic

64. Work with presentation
fetchUser().startWithResult { (result) in
switch result {
case .success(let user):
//save user
case .failure(let error):
//show alert
}
}
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65. Work with presentation
fetchUser().startWithResult { (result) in
switch result {
case .success(let user):
//save user
case .failure(let error):
//show alert
}
}
@EliSawic

66. Work with presentation
fetchUser().startWithResult { (result) in
switch result {
case .success(let user):
//save user
case .failure(let error):
//show alert
}
}
@EliSawic

67. Cold vs Hot
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68. Signal SignalProducer
presentation.observeValues presentation.startWithValues
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69. Signal SignalProducer
presentation.observeValues presentation.startWithValues
emits values all the time waits for your request
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70. // push based
locationUpdates.observeValues { update in
}
// pull based
fetchUser.startWithValues { user in
}
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71. // push based
locationUpdates.subscribe { update in
}
// pull based
fetchUser.subscribe { user in
}
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72. Properties
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73. Mutable Property
let firstSlide = Slide(number: 1)
let slide = MutableProperty<Slide>(firstSlide)
slide.producer.startWithValues { (text) in
print(text)
}
slide.value = Slide(number: 2)
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74. Mutable Property
let firstSlide = Slide(number: 1)
let slide = MutableProperty<Slide>(firstSlide)
slide.producer.startWithValues { (text) in
print(text)
}
slide.value = Slide(number: 2)
@EliSawic

75. Mutable Property
let firstSlide = Slide(number: 1)
let slide = MutableProperty<Slide>(firstSlide)
slide.producer.startWithValues { (text) in
print(text)
}
slide.value = Slide(number: 2)
@EliSawic

76. Mutable Property
let firstSlide = Slide(number: 1)
let slide = MutableProperty<Slide>(firstSlide)
slide.producer.startWithValues { (text) in
print(text)
}
slide.value = Slide(number: 2)
@EliSawic

77. Mutable Property
let firstSlide = Slide(number: 1)
let slideContainer = MutableProperty<Slide>(firstSlide)
slideContainer.producer.startWithValues { (text) in
print(text)
}
slideContainer.value = Slide(number: 2)
@EliSawic

78. Exposing
properties
let firstSlide = Slide(number: 1)
let mutableSlideContainer = MutableProperty<Slide>(firstSlide)
let readOnlySlide = Property(mutableSlideContainer)
exposedSlide.producer.startWithValues { (text) in
print(text)
}
@EliSawic

79. Exposing
properties
let firstSlide = Slide(number: 1)
let mutableSlideContainer = MutableProperty<Slide>(firstSlide)
let readOnlySlide = Property(mutableSlideContainer)
exposedSlide.producer.startWithValues { (text) in
print(text)
}
@EliSawic

80. Exposing
properties
let firstSlide = Slide(number: 1)
let mutableSlideContainer = MutableProperty<Slide>(firstSlide)
let readOnlySlide = Property(mutableSlideContainer)
exposedSlide.producer.startWithValues { (text) in
print(text)
}
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81. Bindings
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82. Binding example
let slideNumber = MutableProperty<Int>(0)
let (slideSignal, _) = Signal<Slide, NoError>.pipe()
slideNumber <~ slideSignal.map { return $0.number }
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83. Binding example
let slideNumber = MutableProperty<Int>(0)
let (slideSignal, _) = Signal<Slide, NoError>.pipe()
slideNumber <~ slideSignal.map { return $0.number }
slideNumber signal
0 -
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84. Binding example
let slideNumber = MutableProperty<Int>(0)
let (slideSignal, _) = Signal<Slide, NoError>.pipe()
slideNumber <~ slideSignal.map { return $0.number }
slideNumber signal
0 -
2 Slide(number: 2)
@EliSawic

85. Reactive extensions
let (slideSignal, _) = Signal<Slide, NoError>.pipe()
label.reactive.text
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86. Reactive extensions
let (slideSignal, _) = Signal<Slide, NoError>.pipe()
label.reactive.text <~ slideSignal.map { return "Slide: ($0.number)" }
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87. Schedulers
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88. Know where you are
signal.observeValues { data in
print("Performing UI updates")
}
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89. Know where you are
signal.observe(on: QueueScheduler.main)
.observeValues { data in
print("Performing UI updates")
}
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90. Memory Management
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91. Disposables
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92. Free your memory
let disposable = locationService.observeValues { update in
// update location
}
disposable.dispose()
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93. Lifetime
let (lifetime, token) = Lifetime.make()
locationService
.take(during: lifetime)
.observeValues { update in
// update location
}
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94. Lifetime
let (lifetime, token) = Lifetime.make()
locationService
.take(during: lifetime)
.observeValues { update in
// update location
}
@EliSawic

95. Lifetime
let (lifetime, token) = Lifetime.make()
locationService
.take(during: lifetime)
.observeValues { update in
// update location
}
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96. Recap
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97. Recap
• Signals / SignalProducers
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98. Recap
• Signals / SignalProducers
• Events
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99. Recap
• Signals / SignalProducers
• Events
• Properties
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100. Recap
• Signals / SignalProducers
• Events
• Properties
• Bindings / Reactive extensions
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101. Recap
• Signals / SignalProducers
• Events
• Properties
• Bindings / Reactive extensions
• Schedulers
@EliSawic

102. Recap
• Signals / SignalProducers
• Events
• Properties
• Bindings / Reactive extensions
• Schedulers
• Disposables / Lifetime
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103. Example
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104. @EliSawic

105. How does it work?
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106. Is name valid?
let isValidNameSignal = nameSignal.map { (name) -> Bool in
return name.characters.count > 2
}
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107. let isValidNameSignal = nameSignal.map { (name) -> Bool in
return name.characters.count > 2
}
nameSignal isValidNameSignal
E false
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108. let isValidNameSignal = nameSignal.map { (name) -> Bool in
return name.characters.count > 2
}
nameSignal isValidNameSignal
E false
El false
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109. let isValidNameSignal = nameSignal.map { (name) -> Bool in
return name.characters.count > 2
}
nameSignal isValidNameSignal
E false
El false
Eli true
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110. let isValidNameSignal = nameSignal.map { (name) -> Bool in
return name.characters.count > 2
}
nameSignal isValidNameSignal
E false
El false
Eli true
Elia true
Elias true
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111. let isValidNameSignal = nameSignal.map { (name) -> Bool in
return name.characters.count > 2
}
nameSignal isValidNameSignal
E false
El false
Eli true
Elia true
Elias true
Eliasz true
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112. Is surname valid?
let isValidSurnameSignal = surnameSignal.map { (surname) -> Bool in
return surname.characters.count > 2
}
@EliSawic

113. Is mail valid?
let isValidMailSignal = mailSignal.map { (mail) -> Bool in
let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,}"
let emailTest = NSPredicate(format:"SELF MATCHES %@", emailRegEx)
return emailTest.evaluateWithObject(mail)
}
@EliSawic

114. let isValidMailSignal = mailSignal.map { (mail) -> Bool in
let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,}"
let emailTest = NSPredicate(format:"SELF MATCHES %@", emailRegEx)
return emailTest.evaluateWithObject(mail)
}
mailSignal isValidMailSignal
a false
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115. let isValidMailSignal = mailSignal.map { (mail) -> Bool in
let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,}"
let emailTest = NSPredicate(format:"SELF MATCHES %@", emailRegEx)
return emailTest.evaluateWithObject(mail)
}
mailSignal isValidMailSignal
a false
a@ false
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116. let isValidMailSignal = mailSignal.map { (mail) -> Bool in
let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,}"
let emailTest = NSPredicate(format:"SELF MATCHES %@", emailRegEx)
return emailTest.evaluateWithObject(mail)
}
mailSignal isValidMailSignal
a false
a@ false
a@b false
@EliSawic

117. let isValidMailSignal = mailSignal.map { (mail) -> Bool in
let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,}"
let emailTest = NSPredicate(format:"SELF MATCHES %@", emailRegEx)
return emailTest.evaluateWithObject(mail)
}
mailSignal isValidMailSignal
a false
a@ false
a@b false
a@b. false
@EliSawic

118. let isValidMailSignal = mailSignal.map { (mail) -> Bool in
let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,}"
let emailTest = NSPredicate(format:"SELF MATCHES %@", emailRegEx)
return emailTest.evaluateWithObject(mail)
}
mailSignal isValidMailSignal
a false
a@ false
a@b false
a@b. false
a@b.c false
@EliSawic

119. let isValidMailSignal = mailSignal.map { (mail) -> Bool in
let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,}"
let emailTest = NSPredicate(format:"SELF MATCHES %@", emailRegEx)
return emailTest.evaluateWithObject(mail)
}
mailSignal isValidMailSignal
a false
a@ false
a@b false
a@b. false
a@b.c false
a@b.cd true
@EliSawic

120. Combine Latest
let formDataSignal = Signal.combineLatest(
isValidNameSignal,
isValidSurnameSignal,
isValidMailSignal)
@EliSawic

121. Combine Latest
let formData = Signal.combineLatest(
name,
surname,
mail)
@EliSawic

122. let formData = Signal.combineLatest(
name,
surname,
mail)
formData name surname mail
@EliSawic

123. let formData = Signal.combineLatest(
name,
surname,
mail)
formData name surname mail
- true - -
@EliSawic

124. let formData = Signal.combineLatest(
name,
surname,
mail)
formData name surname mail
- true - -
- true false -
@EliSawic

125. let formData = Signal.combineLatest(
name,
surname,
mail)
formData name surname mail
- true - -
- true false -
(true,false,true) true false true
@EliSawic

126. let formData = Signal.combineLatest(
name,
surname,
mail)
formData name surname mail
- true - -
- true false -
(true,false,true) true false true
(true,true,true) true true true
@EliSawic

127. Is form valid?
let isValidFormSignal = formDataSignal.map {
(isValidName, isValidSurname, isValidMail) -> Bool in
return isValidMail && isValidSurname && isValidMail
}
@EliSawic

128. let isValidFormSignal = formDataSignal.map {
(isValidName, isValidSurname, isValidMail) -> Bool in
return isValidMail && isValidSurname && isValidMail
}
isValidForm formData
false (true,false,true)
@EliSawic

129. let isValidFormSignal = formDataSignal.map {
(isValidName, isValidSurname, isValidMail) -> Bool in
return isValidMail && isValidSurname && isValidMail
}
isValidForm formData
false (true,false,true)
true (true,true,true)
@EliSawic

130. Update the state
isValidFormSignal.observeValues { isValid in
updateButtonWith(state: isValid)
}
@EliSawic

131. Binding
let isValidForm = MutableProperty<Bool>(false)
isValidForm <~ isFormValidSignal
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132. Reactive everywhere!
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133. Drawbacks
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134. Know the drawbacks
• Another layer for your app
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135. Know the drawbacks
• Another layer for your app
• Learning curve
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136. Know the drawbacks
• Another layer for your app
• Learning curve
• Tricky debugging
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137. Enjoy the pros
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138. Enjoy the pros
• Composable streams
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139. Enjoy the pros
• Composable streams
• Easier asynchronous code
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140. Enjoy the pros
• Composable streams
• Easier asynchronous code
• Works great with MVVM
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141. Stay Reactive
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142. Stay Reactive
sendCompleted()
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143. @Elisawic
www.eliaszsawicki.com
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